1. Field of the Invention
The present invention relates generally to a light beam heating system capable of performing local heating by focusing light from a light source, and more particularly to a light beam heating system suited for use in manufacturing information or communication equipment, electronically controlled equipment, electronic components, transmission components, semiconductors or the like. In manufacturing this equipment or these components, a local soldering process is automated by the use of the light beam heating system according to the present invention.
2. Description of the Prior Art
Light beam heating systems are in wide practical use today as local heating systems without requiring physical contact. In the light beam heating systems, a xenon lamp or a YAG laser diode is generally utilized as a light source, and upon condensing light from the light source, an object to be heated is directly irradiated thereby. Prior to the condensing, the light from the light source may be introduced to a desired location via a light transmission means such as, for example, a fiber cable.
FIG. 1 schematically depicts a conventional light beam heating system wherein a light emitting portion of a lamp 1, for example a xenon lamp, is positioned at a first focal point 3 of an ellipsoidal reflector 2, which condenses light from the lamp 1. The light condensed by the reflector 2 is led to an object 5 to be heated via a light transmission means such as, for example, a fiber cable 6. To this end, the center of one end of the fiber cable 6 is positioned at a second focal point 4 of the reflector 2, and an optical lens assembly 7 for converging or focusing light transmitted by the fiber cable 6 on the object 5 is secured to the other end of the fiber cable 6. The use of the fiber cable 6 is to prevent light reflected by the reflector 2 from adversely affecting electronic components or the like disposed in the proximity of the second focal point 4 of the reflector 2. As a matter of course, the object 5 may be located at the second focal point 4 of the reflector 2 without using the fiber cable 6. The lamp 1 is operatively connected with a power circuit 8, which regulates an input current to the lamp 1, thereby controlling the intensity of light to be irradiated on the object 5.
In the above construction, when the lamp 1 is turned on, the lamp 1 emits light by a preset electric current applied thereto. The light from the lamp 1 is reflected by the reflector 2 and is introduced to the lens assembly 7 via the fiber cable 6. The light is then focused on the object 5 to heat it.
FIG. 2 schematically depicts another conventional light beam heating system having an optical mechanism 17 disposed on a light path between a lamp 1 and a second focal point of an ellipsoidal reflector 2. This light beam heating system is provided with no light transmission means, and the optical mechanism 17 is intended to convert light reflected from the reflector 2 into plural rays of light, which are in turn irradiated on desired points of an object 5 to be heated when a shutter 9 is open.
In the above-described conventional light beam heating systems, however, because the object 5 is heated in the atmosphere, the object 5 tends to be oxidized in the presence of oxygen in the atmosphere.
For example, if the object 5 is a leg of an electronic component, and if the electronic component is desired to be secured to a printed foil with the leg soldered to the component by the use of a soldering paste, the soldering paste often fails to sufficiently wet the leg and the printed foil, resulting in formation of solder balls. Where the amount of flux residue left on the printed circuit board after the soldering is to be minimized so that the use of a solvent such as, for example, flon can be dispensed with in cleansing the printed circuit board to eliminate the necessity of cleansing the printed circuit board, the heating of the soldering paste in the atmosphere often results in a failure of the printed circuit board to be wetted, accompanied by a formation of a substantial number of solder balls. Accordingly, the conventional light beam heating systems have unsolved problems, making it difficult to abolish the use of the solvent.
In any event, the conventional light beam heating system is, in most cases, used to accomplish a soldering of component parts to a printed circuit board after most of the component parts have already been mounted thereon. Accordingly, the heating of the soldering paste often results in the formation of the solder balls.
In order to reduce the length of time during which the heating is carried out, the intensity of light to be irradiated must be increased. However, the higher the light intensity, the more often the formation of the solder balls. Accordingly, the conventional light beam heating system requires a preheating of the object to be heated, rendering the apparatus as a whole to be high in manufacturing cost.